Keeping an invasion force off Greenland would be laughably easy, even trivial, for any country with cruise missiles and bombers because establishing and maintaining a foothold would be so miserably difficult.China is unlikely to physically invade the place and Russia would struggle to fabricate an historical claim. Invasion would be a logistical nightmare for both. Denmark with British/ French support could probably thwart an attack without US support or at least make it prohibitively costly. Mining concessions to China or Russia by Greenlanders asserting independence from USA is more likely threat
In Arctic conditions, logistics dominate combat power. Russia struggles with this even inside its own Arctic territory.
There is no land route to support the logistics of contested invasion, and the sea routes are blocked nine months of the year. The Russians have some icebreakers, but those can't meet the logistics requirement and would be sitting ducks for aircraft launched from the CONUS or carriers in the North Atlantic.
Essentially, establishing and maintaining military forces on Greenland requires a permissive environment.
Upvote
0